The front end structure of an automotive vehicle is designed to provide visual appeal to the vehicle owner while functioning as an energy absorbing structure during frontal and offset crashes. The size, shape and construction of the front end structure contribute to the ability of the front end structure to attenuate the crash pulse and restrict intrusions into the operator's cabin of the vehicle. It is important to design a front end structure to absorb crash energy through the frame components. To that extent, a significant amount of effort by vehicle engineers is devoted to designing the vehicle frame to crush in a controlled manner while absorbing a maximum amount of energy.
One of the goals in the design of vehicle frame structure is to provide better engagement and absorption of energy during a collision. The major components in absorbing energy in frontal as well as rear impacts are the rails. Furthermore, in a side collision if the vehicle has a softer front end it can help mitigate the injuries to occupants in both vehicles. If there is an apparatus to absorb more energy and prolong the time to crush the rails, the crash pulse and intrusion can be reduced significantly.
Vehicle frames typically include an upper rail and a generally vertically spaced lower rail. Preferably, the upper rail joins the lower rail, such as at the forwardmost portion of the vehicle frame, to define an integrally connected automotive frame structure. The structural joint connection between the vehicular upper and lower structural member is conventionally designed as a solid connection which provided good structural integrity in all directions. One approach to the management of crash energy is to reduce the structural efficiency of the joint between the upper and lower rail members in the fore-and-aft direction to allow a “break away” while experiencing a safety load condition. By properly designing the structural joint between the upper and lower rails, the amount of crash energy that would be taken by the lower load path relative to the upper load path can be properly tuned, as well as tune the relative timing in which each load path reaches the passenger compartment. While the formation of the upper and lower rail members is preferably accomplished through hydroforming techniques which forms the upper and lower rails as tubular members, the upper and lower rails can be formed of any material or any construction technique, including stamped and roll formed vehicular body structures.
In U.S. Pat. No. 5,454,453, issued to James Meyer on Oct. 3, 1995, and assigned to Ford Motor Company, the concept of a break-away bracket is used to connect a cross member with the frame rails so that the bracket will deform upon impact and prevent damage to the cross member. U.S. Pat. No. 6,293,618, granted to Akihiro Sukegawa on Sep. 25, 2001, discloses a welding of a center pillar beam and a side sill to form a joint by welding the lower edges of the center pillar with the corresponding mating part of the side sill to provide sufficient strength in this joint to resist intrusion during side impact without using a T-shaped member. Although the Sukegawa patent discloses that the welding distance between the center pillar and the side sill can be changed to provide varying amounts of strength, there does not appear to be any teaching for the welding of this joint to permit breakaway upon impact.
In U.S. Pat. No. 6,499,798, granted to Yorito Takemoto on Dec. 31, 2002, a vehicle body structure is disclosed in which the front side member and kick up portion are welded to each other in a manner so as to be capable of deforming upon impact. Published U.S. Patent Application No. 2004/0046381, published on Mar. 11, 2004, discloses a subframe mounted to a vehicle body through subframe mounts. Certain of the subframe mounts are formed with a fracture stress lower than the fracture stress of the other subframe mounts to enable the subframe to break away from the vehicle body and prevent intrusion of the subframe into the passenger compartment.
Accordingly, it would be desirable to provide a structural joint between two primary frame components in an automotive vehicle to permit the joint to break apart in a fore-and-aft direction in order to tune the amount of crash energy that would be taken by the lower load path relative to the upper load path, as well as the relative timing in which each load path reaches the passenger compartment during an impact situation.